Hybrid inorganic-organic resins may provide higher temperature performance in oxidizing environments than their organic counterparts. Phthalonitrile (PN) polymers are excellent candidates for hybridization due to their high thermal stability and glass transition temperatures and their need for improved long-term oxidative stability and toughness. In this work phenyl-substituted organosilicon linkages were incorporated into PN monomers to investigate their effect on the processing, thermo-mechanical properties, and thermal and oxidative stability. Three hybrid silicon-containing phthalonitrile monomers were synthesized incorporating diphenoxydiphenylsilane, tetraphenylsilane, and hexaphenyldisiloxane moieties. Processability of the polymers was highly dependent on catalyst content and an ideal concentration was determined. The impact on glass transition, coefficient of thermal expansion, stability in TGA, and long-term oxidative stability at 250 °C was evaluated. As-synthesized materials performed significantly better than polymers produced from purified monomers. Degradation of the tetraphenylsilane phthalonitrile monomer was examined in detail via IR-TGA and analysis of aged samples. Multiple degradations were identified involving both the organic and hybrid sections of the polymer. Synthesized materials are compared with commercial phthalonitrile reference materials and to other silicon-phthalonitriles in recent literature. Explanations of behavior and suggestions for future improvements are provided. / PHD / High temperature plastics and plastic composites are needed for electronics and aerospace components. Phthalonitriles (PNs) are one chemistry that shows promise for these applications. PN materials show excellent stability and strength at high temperatures. In this work, the inclusion of silicon-containing linkages into PN plastics was investigated with the intention of improving the properties and long-term stability in air at high temperatures. Three silicon-containing PN compounds were produced. The processing of un-cured resins was characterized and optimized. Resins were then cured at high temperatures. Each polymer’s softening point, thermal expansion, and stability in air and under inert conditions were evaluated. The effect of purity was considered, and it was found that as-produced PN plastics behaved better than highly purified PN plastics. The degradation reactions were studied during long-term exposure to high temperatures and short-term exposure to even higher temperatures. These silicon-containing PN materials were also compared with commercial PN plastics and with other PN literature. Explanations of behavior and suggestions for future improvements are provided.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/87412 |
| Date | 01 February 2019 |
| Creators | Monzel, William Jacob |
| Contributors | Materials Science and Engineering, Lu, Guo Quan, Staley, Thomas W., Suchicital, Carlos T. A., Pruyn, Timothy L., Yee, Gordon T. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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